Honor @Autowired(required=false) at parameter level

Includes a revision of the AutowireCandidateResolver SPI with default methods.

Issue: SPR-15268

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/factory/InjectionPoint.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -111,6 +111,17 @@ public Annotation[] getAnnotations() {
 		}
 	}
 
+	/**
+	 * Retrieve a field/parameter annotation of the given type, if any.
+	 * @param annotationType the annotation type to retrieve
+	 * @return the annotation instance, or {@code null} if none found
+	 * @since 4.3.9
+	 */
+	public <A extends Annotation> A getAnnotation(Class<A> annotationType) {
+		return (this.field != null ? this.field.getAnnotation(annotationType) :
+				this.methodParameter.getParameterAnnotation(annotationType));
+	}
+
 	/**
 	 * Return the type declared by the underlying field or method/constructor parameter,
 	 * indicating the injection type.

spring-beans/src/main/java/org/springframework/beans/factory/annotation/QualifierAnnotationAutowireCandidateResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -309,7 +309,21 @@ protected Annotation getFactoryMethodAnnotation(RootBeanDefinition bd, Class<? e
 
 
 	/**
-	 * Determine whether the given dependency carries a value annotation.
+	 * Determine whether the given dependency declares an autowired annotation,
+	 * checking its required flag.
+	 * @see Autowired#required()
+	 */
+	@Override
+	public boolean isRequired(DependencyDescriptor descriptor) {
+		if (!super.isRequired(descriptor)) {
+			return false;
+		}
+		Autowired autowired = descriptor.getAnnotation(Autowired.class);
+		return (autowired == null || autowired.required());
+	}
+
+	/**
+	 * Determine whether the given dependency declares a value annotation.
 	 * @see Value
 	 */
 	@Override

spring-beans/src/main/java/org/springframework/beans/factory/support/AutowireCandidateResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,30 +32,54 @@ public interface AutowireCandidateResolver {
 	/**
 	 * Determine whether the given bean definition qualifies as an
 	 * autowire candidate for the given dependency.
+	 * <p>The default implementation checks
+	 * {@link org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()}.
 	 * @param bdHolder the bean definition including bean name and aliases
 	 * @param descriptor the descriptor for the target method parameter or field
 	 * @return whether the bean definition qualifies as autowire candidate
+	 * @see org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()
 	 */
-	boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor);
+	default boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
+		return bdHolder.getBeanDefinition().isAutowireCandidate();
+	}
+
+	/**
+	 * Determine whether the given descriptor is effectively required.
+	 * <p>The default implementation checks {@link DependencyDescriptor#isRequired()}.
+	 * @param descriptor the descriptor for the target method parameter or field
+	 * @return whether the descriptor is marked as required or possibly indicating
+	 * non-required status some other way (e.g. through a parameter annotation)
+	 * @since 5.0
+	 * @see DependencyDescriptor#isRequired()
+	 */
+	default boolean isRequired(DependencyDescriptor descriptor) {
+		return descriptor.isRequired();
+	}
 
 	/**
 	 * Determine whether a default value is suggested for the given dependency.
+	 * <p>The default implementation simply returns {@code null}.
 	 * @param descriptor the descriptor for the target method parameter or field
 	 * @return the value suggested (typically an expression String),
 	 * or {@code null} if none found
 	 * @since 3.0
 	 */
-	Object getSuggestedValue(DependencyDescriptor descriptor);
+	default Object getSuggestedValue(DependencyDescriptor descriptor) {
+		return null;
+	}
 
 	/**
 	 * Build a proxy for lazy resolution of the actual dependency target,
 	 * if demanded by the injection point.
+	 * <p>The default implementation simply returns {@code null}.
 	 * @param descriptor the descriptor for the target method parameter or field
 	 * @param beanName the name of the bean that contains the injection point
 	 * @return the lazy resolution proxy for the actual dependency target,
 	 * or {@code null} if straight resolution is to be performed
 	 * @since 4.0
 	 */
-	Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, String beanName);
+	default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, String beanName) {
+		return null;
+	}
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -1090,7 +1090,7 @@ public Object doResolveDependency(DependencyDescriptor descriptor, String beanNa
 
 			Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
 			if (matchingBeans.isEmpty()) {
-				if (descriptor.isRequired()) {
+				if (isRequired(descriptor)) {
 					raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
 				}
 				return null;
@@ -1102,7 +1102,7 @@ public Object doResolveDependency(DependencyDescriptor descriptor, String beanNa
 			if (matchingBeans.size() > 1) {
 				autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
 				if (autowiredBeanName == null) {
-					if (descriptor.isRequired() || !indicatesMultipleBeans(type)) {
+					if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
 						return descriptor.resolveNotUnique(type, matchingBeans);
 					}
 					else {
@@ -1207,6 +1207,10 @@ else if (Map.class == type) {
 		}
 	}
 
+	private boolean isRequired(DependencyDescriptor descriptor) {
+		return this.autowireCandidateResolver.isRequired(descriptor);
+	}
+
 	private boolean indicatesMultipleBeans(Class<?> type) {
 		return (type.isArray() || (type.isInterface() &&
 				(Collection.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type))));

spring-beans/src/main/java/org/springframework/beans/factory/support/GenericTypeAwareAutowireCandidateResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -40,7 +40,8 @@
  * @author Juergen Hoeller
  * @since 4.0
  */
-public class GenericTypeAwareAutowireCandidateResolver implements AutowireCandidateResolver, BeanFactoryAware {
+public class GenericTypeAwareAutowireCandidateResolver extends SimpleAutowireCandidateResolver
+		implements BeanFactoryAware {
 
 	private BeanFactory beanFactory;
 
@@ -57,8 +58,8 @@ protected final BeanFactory getBeanFactory() {
 
 	@Override
 	public boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
-		if (!bdHolder.getBeanDefinition().isAutowireCandidate()) {
-			// if explicitly false, do not proceed with any other checks
+		if (!super.isAutowireCandidate(bdHolder, descriptor)) {
+			// If explicitly false, do not proceed with any other checks...
 			return false;
 		}
 		return (descriptor == null || checkGenericTypeMatch(bdHolder, descriptor));
@@ -166,23 +167,4 @@ protected ResolvableType getReturnTypeForFactoryMethod(RootBeanDefinition rbd, D
 		return null;
 	}
 
-
-	/**
-	 * This implementation always returns {@code null}, leaving suggested value support up
-	 * to subclasses.
-	 */
-	@Override
-	public Object getSuggestedValue(DependencyDescriptor descriptor) {
-		return null;
-	}
-
-	/**
-	 * This implementation always returns {@code null}, leaving lazy resolution support up
-	 * to subclasses.
-	 */
-	@Override
-	public Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, String beanName) {
-		return null;
-	}
-
 }

spring-beans/src/main/java/org/springframework/beans/factory/support/SimpleAutowireCandidateResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,6 @@
 
 package org.springframework.beans.factory.support;
 
-import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.DependencyDescriptor;
 
@@ -27,20 +26,19 @@
  * @author Mark Fisher
  * @author Juergen Hoeller
  * @since 2.5
- * @see BeanDefinition#isAutowireCandidate()
  */
 public class SimpleAutowireCandidateResolver implements AutowireCandidateResolver {
 
-	/**
-	 * Determine if the provided bean definition is an autowire candidate.
-	 * <p>To be considered a candidate the bean's <em>autowire-candidate</em>
-	 * attribute must not have been set to 'false'.
-	 */
 	@Override
 	public boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
 		return bdHolder.getBeanDefinition().isAutowireCandidate();
 	}
 
+	@Override
+	public boolean isRequired(DependencyDescriptor descriptor) {
+		return descriptor.isRequired();
+	}
+
 	@Override
 	public Object getSuggestedValue(DependencyDescriptor descriptor) {
 		return null;

spring-beans/src/test/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessorTests.java

@@ -699,8 +699,7 @@ public void testConstructorResourceInjectionWithMultipleCandidatesAsOrderedColle
 		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
 		bpp.setBeanFactory(bf);
 		bf.addBeanPostProcessor(bpp);
-		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(
-				ConstructorsCollectionResourceInjectionBean.class));
+		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(ConstructorsCollectionResourceInjectionBean.class));
 		TestBean tb = new TestBean();
 		bf.registerSingleton("testBean", tb);
 		FixedOrder2NestedTestBean ntb1 = new FixedOrder2NestedTestBean();
@@ -717,6 +716,46 @@ public void testConstructorResourceInjectionWithMultipleCandidatesAsOrderedColle
 		bf.destroySingletons();
 	}
 
+	@Test
+	public void testSingleConstructorInjectionWithMultipleCandidatesAsOrderedCollection() {
+		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
+		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
+		bpp.setBeanFactory(bf);
+		bf.addBeanPostProcessor(bpp);
+		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(SingleConstructorCollectionInjectionBean.class));
+		TestBean tb = new TestBean();
+		bf.registerSingleton("testBean", tb);
+		FixedOrder2NestedTestBean ntb1 = new FixedOrder2NestedTestBean();
+		bf.registerSingleton("nestedTestBean1", ntb1);
+		FixedOrder1NestedTestBean ntb2 = new FixedOrder1NestedTestBean();
+		bf.registerSingleton("nestedTestBean2", ntb2);
+
+		SingleConstructorCollectionInjectionBean bean = (SingleConstructorCollectionInjectionBean) bf.getBean("annotatedBean");
+		assertSame(tb, bean.getTestBean());
+		assertEquals(2, bean.getNestedTestBeans().size());
+		assertSame(ntb2, bean.getNestedTestBeans().get(0));
+		assertSame(ntb1, bean.getNestedTestBeans().get(1));
+		bf.destroySingletons();
+	}
+
+	@Test
+	public void testSingleConstructorInjectionWithEmptyCollection() {
+		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver());
+		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
+		bpp.setBeanFactory(bf);
+		bf.addBeanPostProcessor(bpp);
+		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(SingleConstructorCollectionInjectionBean.class));
+		TestBean tb = new TestBean();
+		bf.registerSingleton("testBean", tb);
+
+		SingleConstructorCollectionInjectionBean bean = (SingleConstructorCollectionInjectionBean) bf.getBean("annotatedBean");
+		assertSame(tb, bean.getTestBean());
+		assertNull(bean.getNestedTestBeans());
+		bf.destroySingletons();
+	}
+
 	@Test
 	public void testConstructorResourceInjectionWithMultipleCandidatesAndFallback() {
 		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
@@ -2757,6 +2796,28 @@ public List<NestedTestBean> getNestedTestBeans() {
 	}
 
 
+	public static class SingleConstructorCollectionInjectionBean {
+
+		private ITestBean testBean;
+
+		private List<NestedTestBean> nestedTestBeans;
+
+		public SingleConstructorCollectionInjectionBean(ITestBean testBean,
+				@Autowired(required = false) List<NestedTestBean> nestedTestBeans) {
+			this.testBean = testBean;
+			this.nestedTestBeans = nestedTestBeans;
+		}
+
+		public ITestBean getTestBean() {
+			return this.testBean;
+		}
+
+		public List<NestedTestBean> getNestedTestBeans() {
+			return this.nestedTestBeans;
+		}
+	}
+
+
 	@SuppressWarnings("serial")
 	public static class MyTestBeanMap extends LinkedHashMap<String, TestBean> {
 	}